1. Field of Endeavor
The present invention relates to voice coding and more particularly to ultra-narrow bandwidth voice coding.
2. State of Technology
U.S. Pat. No. 5,729,694 for speech coding, reconstruction and recognition using acoustics and electromagnetic waves to John F. Holzrichter and Lawrence C. Ng, issued Mar. 17, 1998 provides the following background information, “The history of speech characterization, coding, and generation has spanned the last one and one half centuries. Early mechanical speech generators relied upon using arrays of vibrating reeds and tubes of varying diameters and lengths to make human-voice-like sounds. The combinations of excitation sources (e.g., reeds) and acoustic tracts (e.g., tubes) were played like organs at theaters to mimic human voices. In the 20th century, the physical and mathematical descriptions of the acoustics of speech began to be studied intensively and these were used to enhance many commercial products such as those associated with telephony and wireless communications. As a result, the coding of human speech into electrical signals for the purposes of transmission was extensively developed, especially in the United States at the Bell Telephone Laboratories. A complete description of this early work is given by J. L. Flanagan, in “Speech Analysis, Synthesis, and Perception,” Academic Press, N.Y., 1965. He describes the physics of speech and the mathematics of describing acoustic speech units (i.e., coding). He gives examples of how human vocal excitation sources and the human vocal tracts behave and interact with each other to produce human speech. The commercial intent of the early telephone work was to understand how to use the minimum bandwidth possible for transmitting acceptable vocal quality on the then-limited number of telephone wires and on the limited frequency spectrum available for radio (i.e., wireless) communication. Secondly, workers learned that analog voice transmission uses typically 100 times more bandwidth than the transmission of the same word if simple numerical codes representing the speech units such as phonemes or words are transmitted. This technology is called ‘Analysis-Synthesis Telephony’ or ‘Vocoding.’”
U.S. Pat. No. 6,463,407 for low bit-rate coding of unvoiced segments of speech by Amitava Das and Sharath Manjunath issued Oct. 8, 2002 and assigned to Qualcomm, Inc. provides the following background information, “Transmission of voice by digital techniques has become widespread, particularly in long distance and digital radio telephone applications. This, in turn, has created interest in determining the least amount of information that can be sent over a channel while maintaining the perceived quality of the reconstructed speech. If speech is transmitted by simply sampling and digitizing, a data rate on the order of sixty-four kilobits per second (kbps) is required to achieve a speech quality of conventional analog telephone. However, through the use of speech analysis, followed by the: appropriate coding, transmission, and resynthesis at the receiver, a significant reduction in the data rate can be achieved. Devices that employ techniques to compress speech by extracting parameters that relate to a model of human speech generation are called speech coders. A speech coder divides the incoming speech signal into blocks of time, or analysis frames. Speech coders typically comprise an encoder and a decoder, or a codec. The encoder analyzes the incoming speech frame to extract certain relevant parameters, and then quantizes the parameters into binary representation, i.e., to a set of bits or a binary data packet. The data packets are transmitted over the communication channel to a receiver and a decoder. The decoder processes the data packets, unquantizes them to produce the parameters, and then resynthesizes the speech frames using the unquantized parameters.”